Acne is normally caused by an over-production of sebum that clogs the pores. Sebum is released into the pores on a regular basis, but certain hormones cause an over production such as testosterone and the stress hormone cortisol. Any increase in these hormones corresponds to an increase of acne on the skin.
By exercising, you can correct hormonal imbalances that lead to acne. Exercising relieves stress and lowers cortisol levels in the blood, therefore, eliminating the over production of sebum, which can lead to blocked pores. Additionally, exercising creates sweat. Sweat cleans out pores and removes dead skin cells, oils, and chemicals, which build up over time. By flushing out these toxins, you remove existing acne and also impede any further inflammation that the body has to foreign particles on the skin.